Millimeter Emission Structure in the AU Mic Debris Disk

Transcription

1 Millimeter Emission Structure in the AU Mic Debris Disk Meredith MacGregor Harvard University Wilner, D.J., Rosenfeld, K.A., Andrews, S.M., Ma7hews, B., Hughes, A.M., Booth, M., Chiang, E., Graham, J.R., Kalas, P., Kennedy, G., Sibthorpe, B.

2 The Source: AU Mic Member of the β Pictoris Moving Group (9.91 pc, M star, ~12 Myr old) Edge- on geometry Fitzgerald et al. (2007) SB profile steepens in the outer disk For AU Mic, break occurs at r break ~ AU Inferred H 2 - to- dust rayos of 1/30 : 1 (France et al., 2007) Liu (2004)

3 Birth Ring Theory Larger planetesimals collide to produce micron- sized dust grains in a collisional cascade Debris Disk Birth Ring Inner disk is empded by CPR drag and grain- grain collisions SWR forces blow out dust grains from inner birth ring to outer disk Strubbe & Chiang (2006); Augereau & Beust (2006)

4 Observations with the SMA Wavelength: 1.3 mm Synthesized beam: ~ 3 (30 AU) rms: 0.4 mjy beam 1 Adopted a parametric modeling scheme by fieng the visibiliyes directly Wilner et al. (2012)

5 Modeling Results Wilner et al. (2012) Results are consistent with theory Parameter Fits: R cen = 36 (+7 / - 16) AU ΔR =10 (+13 / - 8) AU F = 8.0 ± 1.2 mjy

6 New ALMA Observations MacGregor et al. (2013) Observed at 1.3 mm (Band 6) Two- hour scheduling block executed four Ymes rms of 30 μjy beam 1 Number of operayonal antennas: Synthesized beam: (8 7 AU) ALMA Project S (Wilner), S (Ertel)

7 Modeling Formalism Axisymmetric belt characterized by an annulus with radial intensity: R out I (r) / r x for R in < r < R out NormalizaYon given by: Z F belt = I d r R in Added a circular Gaussian to describe central component F belt Adopted a Monte Carlo Markov Chain (MCMC) approach

8 Modeling Results MacGregor et al. (2013) Best- fit model has two disdnct components: 1. An edge- on outer belt with an emission profile that rises with radius out to 40 AU 2. An unresolved peak at the center of the outer belt

9 Modeling Results Outer Belt Central Peak

10 The Outer Dust Belt PosiDon of far edge well constrained at R out = 40 AU Outer belt parameters are in good agreement with the less well- constrained SMA fits Matches closely outer edge of hypotheycal birth ring Kuiper Belt- like truncadon of outer edge Rising emission profile with radial power- law index x 2.3 ± 0.3 Implies rising surface density profile Inner collisional depleyon? (Kennedy & Wya7, 2010) No detectable asymmetries or substructure SYll consistent with a Uranus- like planet (MusYll & Wya7, 2009)

11 The Central Peak Stellar photosphere at 1.3 mm much fainter than observed flux from central peak Stellar model predicts F * = 52 µjy, ~6x fainter than observed flux Flares detected at ~ µjy at 6 cm Should have fast decay Ymes (~1 hour) Peak persists in all four ALMA SBs, but spectral index constraints are not good enough to be diagnosyc Stellar Corona? Could be tested with the VLA Unresolved inner planetesimal belt within 3 AU of the star Temperature esymates from SED modeling comparable to expected for dust a few AU from the star

12 Summary 1. Birth ring theory explains AU Mic sca7ered light observayons 2. Millimeter observayons with the SMA reveal birth ring of planetesimals 3. ALMA provides a clearer view of the millimeter disk structure 4. Future ALMA observayons will determine nature of central component

13 β Pictoris Golimowski et al. (2006) Original example of break in the surface brightness profile indicayve of birth ring

14 Type B condiyons: dominated by grain- grain collisions Winds dominate in the case of AU Mic as opposed to radiayon pressure in the case of β Pic Inferred H 2 - to- dust rayos of 1/30 : 1 (France et al., 2007) Birth Ring Theory Strubbe & Chiang (2006)

15 MCMC Modeling Special case: IniYal parameter values far from actual

16 MCMC Modeling Base Model: well- constrained fits

17 MCMC Modeling Comparison between a limit and a well- constrained fit

18 The Central Peak- Dust Liu et al. (2004) AU Mic Constrained the extent of the belt to R cen 3 AU (3σ) EsYmated the highest temperature of this inner belt based upon what can be accommodated by the SED For larger grains (a max 1 mm), can fit up to T 75 K Comparable to expected temperature for dust a few AU from the star